Author Topic: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION  (Read 74536 times)

Online abaddon

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Not the track record so far... CRS flights have been incredibly supportive of the changes and development efforts.  The folks over at Commercial crew should watch and learn.
IIRC NASA has previously requested, maybe more than once, not to be the first flight after a big change.  For example F9 1.1, RTF after CRS-7, RTF after Amos-6, first flight using new load procedure with sub-cooled prop.  None of these were CRS flights.  They're also sluggish on getting on-board with using a previously flown booster.  Not that any of that is bad, but they are definitely not first adopters when it comes to CRS (COTS was a different matter).

The folks at Commercial Crew are, I think, just fine...

Offline AncientU

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Not the track record so far... CRS flights have been incredibly supportive of the changes and development efforts.  The folks over at Commercial crew should watch and learn.
IIRC NASA has previously requested, maybe more than once, not to be the first flight after a big change.  For example F9 1.1, RTF after CRS-7, RTF after Amos-6, first flight using new load procedure with sub-cooled prop.  None of these were CRS flights.  They're also sluggish on getting on-board with using a previously flown booster.  Not that any of that is bad, but they are definitely not first adopters when it comes to CRS (COTS was a different matter).

The folks at Commercial Crew are, I think, just fine...

We'll see on reused boosters... if NASA accepts a flight-proven booster for CRS within the first year they are flying, that will be incredibly supportive from an organization that nominally works in decades.  IIRC, SpaceX had re-flown two boosters before NASA began talking about the process they needed to start up to investigate/qualify such usage.
« Last Edit: 08/18/2017 09:00 PM by AncientU »
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Online abaddon

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We'll see on reused boosters... if NASA accepts a flight-proven booster for CRS within the first year they are flying, that will be incredibly supportive from an organization that nominally works in decades.
Not really, three to potentially as many as six or more successful flights of previously-flown boosters would be similar to other certifications NASA has made of the other provider(s) in LSP for higher-value payloads.  And clearly NASA and the CRS program has a lot of insight into Falcon 9 at this point, in combination with CCS.  In fact they stressed how much work they are doing in combination with SpaceX with regards to reviewing the data and paperwork on recovered boosters, what SpaceX is doing to refurbish them, which parts they replace and which ones they don't, etc.

Again, nothing wrong here but let's not fall over ourselves either.  Commercial customers like SES are the ones who are allowing SpaceX to push the envelope with booster reuse.  NASA we can thank for awarding the COTS/CRS contracts that made SpaceX a viable concern, back when they almost folded, as well as working with them to produce a better more reliable product over time, providing expertise in incident reviews, selecting them as a CC provider, selecting them for some lower-risk LSP missions, etc.
« Last Edit: 08/18/2017 09:09 PM by abaddon »

Offline rcoppola

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #223 on: 08/18/2017 09:21 PM »
Once Block 5 is in full rotation and a few are brought back and reflown to validate re-use certification models/processes, this all becomes much easier for NASA and DOD and commercial clients for that matter. So barring any unforeseen Block 5 incidents, I think 2018 is the year that reuse becomes fully operational, transparent, formalized/certified and fully accepted/enjoined industry wide. And thus, the first game, set, match goes to SpaceX.

Let's see if anyone besides BO cares to challenge for the next one...
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Offline georgegassaway

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #224 on: 08/18/2017 09:40 PM »
Meanwhile, as NASA and DOD uses new F9's for their flights, those boosters, assuming they land safely, can be reflown for other customers. 

Only really a serious issue if SpaceX wanted to build fewer new boosters than NASA and DOD wanted to fly aboard. SpaceX would have to get a lot of reflights out of each booster before that's much of a problem.

So far, only 2 re-flights, both with "hot" re-entries which makes it unlikely those boosters will ever fly again. If they wanted to establish that a booster could say re-fly 5 times, they'd want to do it with mild re-entries. Perhaps they will shoot for that once Block 5 is operational, and could be why they didn't do milder re-entries with the two re-flights since those are not B-5's.

Theory and plans are one thing (FH in "6 months" TM), proven record of boosters re-flying 5 to 10 times each without a problem..... not going to see that established for years (flight rate and refurbishment time, even if things go well).

Totally understandable that some customers, such as NASA and DOD, would want to see proof with a real track record.

Just sayin'.....
« Last Edit: 08/18/2017 09:43 PM by georgegassaway »

Offline AncientU

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #225 on: 08/18/2017 10:16 PM »
That's possible... and NASA and DOD will forfeit their 'leadership' role.
They will still have the biggest checkbooks, so all will continue to kowtow to them, but all will know...
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Offline RedLineTrain

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #226 on: 08/18/2017 10:23 PM »
So far, only 2 re-flights, both with "hot" re-entries which makes it unlikely those boosters will ever fly again.

Is that your supposition, or is this based on information provided by SpaceX?

Offline jpo234

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #227 on: 08/18/2017 11:02 PM »


So far, only 2 re-flights, both with "hot" re-entries which makes it unlikely those boosters will ever fly again.

Is that your supposition, or is this based on information provided by SpaceX?

We know that the first reflown booster will be put on display at the CCAFS.
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Offline Robotbeat

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  May have been the 1.7Mlb-f version just flown below the new maximum thrust level though.  Not necessarily inconsistent to have info saying that CRS-12 flew with up-rated engines and data showing that the launch didn't, assuming the higher maximum, use full thrust. 
You don't fly higher-thrust engines for the first time if you do not intend to utilize that higher thrust.
This is not obvious to me.  At some point you start qualifying your engines to a new, higher, maximum thrust.  You incorporate the new engines into new boosters as they are built.   Now suppose the first mission for the new booster does not require the new maximum thrust.   What are you going to do?   Use the new maximum thrust just because you can?  That seems wrong, running at higher ratings surely increases the risk.  Swap if for a booster with crappier engines?  That seems wrong too.

I believe the Shuttle had engine settings which were developed, and qualified, but never intended to be used.  They were reserved for abort scenarios.
Every time SpaceX introduced more powerfull engines on their rockets they immediately made use of the increased power. There is no valid reason not to do so.
They flew Merlin 1C at partial thrust on Falcon 1 because it wasn't yet qualified for fuller thrust (that'd be for Falcon 1e, which never flew).
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Offline Norm38

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #229 on: 08/19/2017 05:14 AM »
Is it better to push the corners, or demonstrate cycle rate?  Push the corners first, then cycle at the corners.
Of course, they have the numbers to cycle a LEO booster and a GTO.

Offline Bananas_on_Mars

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  May have been the 1.7Mlb-f version just flown below the new maximum thrust level though.  Not necessarily inconsistent to have info saying that CRS-12 flew with up-rated engines and data showing that the launch didn't, assuming the higher maximum, use full thrust. 
You don't fly higher-thrust engines for the first time if you do not intend to utilize that higher thrust.
This is not obvious to me.  At some point you start qualifying your engines to a new, higher, maximum thrust.  You incorporate the new engines into new boosters as they are built.   Now suppose the first mission for the new booster does not require the new maximum thrust.   What are you going to do?   Use the new maximum thrust just because you can?  That seems wrong, running at higher ratings surely increases the risk.  Swap if for a booster with crappier engines?  That seems wrong too.

I believe the Shuttle had engine settings which were developed, and qualified, but never intended to be used.  They were reserved for abort scenarios.
Every time SpaceX introduced more powerfull engines on their rockets they immediately made use of the increased power. There is no valid reason not to do so.
They flew Merlin 1C at partial thrust on Falcon 1 because it wasn't yet qualified for fuller thrust (that'd be for Falcon 1e, which never flew).

On missions where you don't need the extra performance, maybe they simply reserve the uprated thrust for engine-out scenarios?
With the uprated thrust, they still might be able to recover a stage if the affected engine(s) are not the 3 restartable ones.
At least in the past, i think an engine-out scenario would almost always result in loss of the first stage because it would use up their landing fuel reserves.

Online macpacheco

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On missions where you don't need the extra performance, maybe they simply reserve the uprated thrust for engine-out scenarios?
With the uprated thrust, they still might be able to recover a stage if the affected engine(s) are not the 3 restartable ones.
At least in the past, i think an engine-out scenario would almost always result in loss of the first stage because it would use up their landing fuel reserves.
There are several flaws in this thinking.
1 - SpaceX knows engine margins, you and I DON'T

2 - The more thrust you use on the first stage, except for the throttle down during MaxQ, the least gravity losses you get, which gives you much better margins should an engine failure happen later. A more lofted trajectory can be used, resulting in a higher altitude separation, with marginally lower horizontal speeds.

3 - The assumption that SpaceX is somehow reducing its safety margins, just because thrust is higher seems intuitive and maybe true, but its likely wrong. The last time a Merlin failed was still first generation Falcons with their M1Cs. So far M1D SL/Vac have a perfect safety track. I think the total safety margin is huge, otherwise SpaceX wouldn't be telling us that all engines that landed were fine for reuse (I suspect the parts requiring substantial refurb are mostly or exclusively related to areas that get little heating on the way up but get lots of heating on the way down, M1D was designed with margin for extensive reuse from the start).

Its perfectly possible both scenarios where CRS12 wasn't a full Block IV booster yet or that it had the higher thrust but NASA simply said: we're fine with old thrust levels, we don't want to risk being the first ones, but once you demonstrate 2 launches at higher thrust, then we're on board. There isn't enough data to conclude it either way.

Engineering is done with sufficient safety margins. If it breaks at thrust x on ground testing, something like 10 or even 20% lower thrust is used. By requalifying M1Ds for higher thrust, SpaceX either didn't have the capability (or didn't have the need to use higher thrust at the time) to break at higher thrust than now or they simply managed to run at higher thrust levels with some changes. I truly doubt SpaceX is reducing safety margins by using higher thrust. Running at much higher safety margins might not appreciably increase safety margins, much like running your car at 50% or 75% power levels doesn't destroy the engine either way (as long as proper maintenance is performed). Aviation engines are routinely run at 100% power for hours at a time, the difference between 100% and 75% power being used most of the time is the overhaul bill rather than time to engine destruction.

Its always fun to speculate wildly, but its also hugely unproductive, and very likely to lead to wildly incorrect conclusions.
« Last Edit: 08/19/2017 04:20 PM by macpacheco »
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Offline Craftyatom

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #232 on: 08/19/2017 06:01 PM »
Not to break up discussion about thrust ratings, but I saw something in the full launch-to-landing telephotography video that I wanted to point out, in case anyone missed it.  Starting at 6:44, and ending at 6:47 (you might want to slow the video down to get a good look), a ring of 8 shock trails form between the engines and over legs, coinciding with the booster going transonic.

At first I thought this was exhaust from engine startup, especially given that it ends almost exactly as the engine starts.  However, it seems too uniform and too far up the booster to be coming from the center engine, the only one that lights during this burn.  Furthermore, similar effects form around the grid fins, and engine ignition changes the environment around the base of the rocket anyways, so it makes sense that it would end such formations.

I love formations like these, and this is a really interesting one - the incoming airflow being squeezed between the eight outer engines produces a pattern that you probably won't find anywhere else!
« Last Edit: 08/19/2017 06:05 PM by Craftyatom »
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Offline Danny452

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #233 on: 08/20/2017 12:37 PM »
"Continuous Close Up Footage of Launch Through Landing of the CRS-12 Falcon 9!" from Astronomy Live:



This video from the Updates thread shows a fast flip of the first stage with a main engine starting before the flip is complete.  The flip must throw propellant to the top of the tanks.  Do the nitrogen thrusters provide ullage?  Or does TEA/TEB give the necessary thrust as well as lighting the engine?  Or is there some other mechanism?

Offline jpo234

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #234 on: 08/20/2017 12:44 PM »
Regarding thrust: Higher thrust means higher G-forces, right? How much can the mice take?
« Last Edit: 08/20/2017 12:44 PM by jpo234 »
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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #235 on: 08/20/2017 11:07 PM »
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Offline whitelancer64

Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #236 on: 08/20/2017 11:18 PM »
"Continuous Close Up Footage of Launch Through Landing of the CRS-12 Falcon 9!" from Astronomy Live:



This video from the Updates thread shows a fast flip of the first stage with a main engine starting before the flip is complete.  The flip must throw propellant to the top of the tanks.  Do the nitrogen thrusters provide ullage?  Or does TEA/TEB give the necessary thrust as well as lighting the engine?  Or is there some other mechanism?

As far as I know, the Nitrogen thrusters do provide ullage. It's hard to tell because the 2nd stage is firing, but it looks to me like the thrusters were firing prior to 1st stage re-ignition for the boost-back burn.
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Offline jpo234

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #237 on: 08/20/2017 11:20 PM »


Regarding thrust: Higher thrust means higher G-forces, right? How much can the mice take?

Ping! Could it be, that SpaceX had to hold back the higher thrust of Block 4 so that they didn't flatten the mice?
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Offline Jim

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #238 on: 08/21/2017 12:23 AM »


Regarding thrust: Higher thrust means higher G-forces, right? How much can the mice take?

Ping! Could it be, that SpaceX had to hold back the higher thrust of Block 4 so that they didn't flatten the mice?

no, because they throttle the engines before MECO

Offline envy887

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Re: SpaceX Falcon 9 : CRS-12 : Aug 14, 2017 : DISCUSSION
« Reply #239 on: 08/21/2017 02:59 AM »
G forces are not an issue in the early part of launch, where extra thrust would be most useful but wasn't observed.

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